We have proposed that nitroaromatic anion free radicals (RNO2) covalently bind with glutathione, protein or with other tissue macromolecules, RNO2 plus P yields RNO2 minus P where P represents a macromolecule or glutathione. In most studies on the covalent binding of reductive intermediates of nitro compounds to protein it is usually assumed that the hydroxylamine metabolite is the metabolite that covalently binds. Yet there is only very circumstantial evidence to support this assumption. Since as much as 14% of a reductive intermediate of some nitrofurans becomes covalently bound to protein, it should be possible to observe spectroscopically the covalent binding of the anion radicals, if this intermediate is indeed responsible for binding. Because reduced glutathione depletion is thought to be important in some drug toxicities, it is important to determine if the anion radical can directly bind to glutathione. In addition, L-cysteine or GSH decreased the covalent binding of one nitrofuran carcinogen by 99.9% without affecting the microsomal nitroreductase activity. Just recently the binding of a reductive metabolite(s) of two nitrofurans to DNA and RNA has been reported.